Portable communication devices, such as cellular telephones, portable computers, personal digital assistants (PDAs), global positioning system (GPS) receivers, and the like, are configured to communicate over wireless networks. Such portable communication devices may enable communication over multiple networks, and therefore include transmitters, receivers and corresponding filters in multiplexers, connecting the receivers and transmitters to a common antenna, for sending and receiving signals (e.g., radio frequency (RF) signals) over various wireless networks.
The multiplexer interfaces between the antenna and each of the networks to enable transmitting signals on different transmit (uplink) frequencies and receiving signals on different receive (downlink) frequencies. The filters associated with the multiplexer include band pass filters and band rejection (or notch) filters. The band pass filters provide passbands for passing various transmitted and received signals through relatively narrow frequency bands (blocking all signals with frequencies outside the passbands), while the notch filters provide stopbands for blocking various transmitted and received signals in relatively narrow frequency bands (passing all signals with frequencies outside the stopbands). The band pass filters and notch filters may be used in a complementary fashion, such that notch filter(s) associated with a first network have stopband(s) that correspond to (e.g., match) passband(s) of band pass filters(s) associated with a second network. In this manner, the likelihood of the signals of the second network passing through the band pass filter interfering with the signals of the first network is greatly reduced.
Conventional multiplexers providing band pass and notch filters for different networks, as shown in FIGS. 3 and 4, tend to have complicated designs with high insertion loss. Examples of conventional multiplexer devices are discussed below with reference to FIGS. 3 and 4. Referring to FIGS. 3 and 4, each band pass filter corresponding to a particular network has an associated notch filter that provides a stopband corresponding to the pass band of the band pass filter. In FIG. 3, the notch filters are arranged in a cascading topology, and in FIG. 4, the notch filters are arranged in a series topology. However, a multiplexer device with less insertion loss caused by the arrangement of band pass and notch filters is desirable.